Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-07-25
2003-07-29
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C156S329000, C428S429000, C525S100000, C525S101000
Reexamination Certificate
active
06599967
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to sheet- or tape-shaped pressure-sensitive adhesive sheets, which are used mainly to fix a functional film to a display device.
2. Description of the Related Art
Pressure-sensitive adhesive sheets have recently been utilized in various fields because of good bonding operation properties. Among these, pressure-sensitive adhesive sheets comprising, as a base component, a homopolymer or copolymer of a monomer containing, as a base, an acrylic polymer (i.e. an alkyl (meth)acrylate) are superior in durability performances such as weathering resistance, heat resistance, deterioration resistance and the like. Therefore, they are used particularly preferably in the fields where these durability performances are required.
As one of uses of pressure-sensitive adhesive sheets, for example, there has been known a use of bonding/fixing functional films such as conductive film, antiglare film and the like to a display device (glass surface thereof). In view of use such as display device to which severe requirements on the appearance is made, it is required for these pressure-sensitive adhesive sheets to cause neither lifting nor formation of bubbles at the bonding interface when exposed to severe conditions such as UV rays for a long time, not to mention at the beginning of standing after bonding/fixing, thus making it possible to maintain good appearance.
Further, in a case a functional film such as an electroconductive film, an anti-glare film or the like included foreign matter, bubbles etc. bonding/fixing the functional film to (the glass surface of) a display or the film is hurt during sticking operation, it is necessary to release this film and bonding/fixing another film. Then, there is demand for re-workability of the pressure-sensitive adhesive by which the adhesive does not remain on the glass surface upon release.
To resolve these requirements, for maintenance of appearance, it is suggested to use acrylic pressure-sensitive adhesive sheets comprising an acrylic polymer, as a base component, and a silane-coupling agent incorporated into the acrylic polymer, thereby to improve the adhesion to the glass surface. Although use of the pressure-sensitive adhesive sheets improves the adhesion to glass to some extent, there still remains such a problem that lifting and formation of bubbles occur at the bonding interface when exposed to severe conditions such as described above, thus making it hard to maintain good appearance.
As a pressure-sensitive adhesive sheet resolving the problem described above, the present inventors have previously proposed a pressure-sensitive adhesive sheet comprising a crosslinked pressure-sensitive adhesive, which is formed by an acrylic polymer, a silane-coupling agent and a crosslinking agent, containing a sol component having specific distribution of molecular weights with less low-molecular components. By this constitution, good appearance can be maintained for a long period of time without lifting or generating bubbles on the adhesive interface even under the above-described severe conditions. Together with this maintenance of appearance, the re-workability mentioned above can however not be satisfied.
SUMMARY OF THE INVENTION
In light of the circumstances described above, an object of the present invention is to provide pressure-sensitive adhesive sheets for fixing a functional film to a display device, having excellent weathering resistance which cause neither lifting nor formation of bubbles at the bonding interface even when exposed to severe conditions such as UV rays for a long time, and satisfying re-workability by which the pressure-sensitive adhesive upon removal does not remain on the glass surface of the functional film.
To achieve this object, the present inventors made extensive study, and as a result, the present inventors have found that in preparing the inventors' previously produced pressure-sensitive adhesive sheet, that is, the pressure-sensitive adhesive sheet comprising a crosslinked pressure-sensitive adhesive, which is formed by an acrylic polymer, a silane-coupling agent and a crosslinking agent, containing a sol component having specific distribution of molecular weights with less low-molecular components, a surfactant along with the silane-coupling agent is incorporated into the acrylic polymer so as to adjust and suitably weaken the adhesion thereof to glass, whereby a pressure-sensitive adhesive sheet not only maintaining good appearance under severe conditions but also satisfying re-workability can be obtained, thus completing the present invention.
That is, the present invention is directed to a pressure-sensitive adhesive sheet comprising a layer of a crosslinked pressure-sensitive adhesive, which is formed by 100 parts by weight of a homopolymer or a copolymer of a monomer containing an alkyl (meth) acrylates as a principal component, 0.001 to 5 parts by weight of a silane-coupling agent, 0.001 to 5 parts by weight of a surfactant and a crosslinking agent, wherein a sol component of the crosslinked pressure-sensitive adhesive has a weight-average molecular weight of not less than 300,000 and a proportion of a low-molecular component having a molecular weight of not more than 100,000 in the sol component is not more than 15% by weight in the measurement of the molecular weight by the gel permeation chromatography method. Also the present invention is directed to a method of fixing a functional film, which comprises bonding/fixing the functional film to a display device through the pressure-sensitive adhesive sheets with the constitution described above.
As used herein, the sol component of the layer of the crosslinked pressure-sensitive adhesive refers to a sol component which is a soluble polymer dissolved in ethyl acetate when a predetermined amount Mo (about 0.5 g) of the above layer is covered with a fluororesin film having numerous pores (diameter: 0.2 &mgr;m), followed by dipping in ethyl acetate at 20° C. for 240 hours. The sol fraction thereof is determined by calculating from the formula: (Mt/Mo)×100 (% by weight) where Mt is an amount of the sol component and Mo is an initial weight before dipping.
Using the above soluble polymer (sol component), the weight-average molecular weight of the sol component and the proportion (% by weight) of the low-molecular component having a molecular weight of not more than 100,000 were determined from a molecular weight distribution curve by the gel permeation chromatography method (hereinafter referred to as the GPC method). The measuring conditions of the molecular weight distribution curve by the GPC method are as follows: concentration of sample; 1 mg/ml, amount of sample introduced; 500 mg, column temperature; 40° C., and flow rate; 1.0 ml/minute.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The acrylic polymer used as the base polymer in the present invention is a homopolymer or copolymer of a monomer containing an alkyl (meth)acrylate as a principal component, and the other monomer, capable of copolymerizing with the alkyl (meth)acrylate, can be used in combination with the alkyl (meth)acrylate.
The alkyl (meth)acrylate is a monomer represented by the following general formula:
wherein R
1
is a hydrogen atom or a methyl group, and R
2
is an alkyl group having 1 to 18 carbon atoms. Specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, lauryl (meth)acrylate and the like.
The copolymerizable monomer, for example, there can be used any of various monomers, which are known as a monomer for modification of an acrylic pressure-sensitive adhesive, such as vinyl acetate, styrene, (meth)acrylonitrile, (meth)acrylamide, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycidyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate and the like. These copolymerizable monomers are u
Kishioka Hiroaki
Ohura Masahiro
Knobbe Martens Olson & Bear LLP
Lipman Bernard
Nitto Denko Corporation
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